The present invention relates to a process for producing low haze heavy base oil from a waxy feed.
Various processes for dewaxing petroleum distillates are well known. The higher molecular weight straight chain normal, substituted and slightly branched paraffins present in lubricating oils are waxes that cause high pour points, high cloud points, and high haze points in the resulting lube oils. If adequate pour points, low haze, and low cloud points are to be obtained in lube oils, the waxes must be wholly or partially removed or converted. In the past, various solvent dewaxing techniques were employed; however, these techniques have high operating costs and significant environmental impacts. Today, catalytic dewaxing processes are used that are more economical and that remove the waxes by selectively isomerizing and/or cracking paraffinic components.
For example, European Patent Application No. 225,053 discloses a process for producing lubricant oils of low pour point and high viscosity index by partially dewaxing a lubricant base stock by isomerization dewaxing followed by a selective dewaxing step. The isomerization dewaxing step is carried out using a large pore, high silica zeolite dewaxing catalyst which isomerizes the waxy components of the base stock to less waxy branch chain isoparaffins. The selective dewaxing step may be either a solvent, e.g., MEK dewaxing operation or a catalytic dewaxing, preferably using a highly shape selective zeolite such as ZSM-22 or ZSM-23.
U.S. Pat. No. 6,051,129 discloses a dewaxing process for lowering the haze point of a bright stock which includes contacting a bright stock in the presence of added hydrogen gas with a Zeolite EU-1 catalyst in combination with a ZSM-48 and/or SSZ-32 catalyst.
Some lube oil streams, particularly heavy streams such as Bright Stock, contain naturally-occurring haze precursors that are more difficult to remove by conventional dewaxing than are the paraffinic waxes that predominate in lower boiling streams. If present in sufficient quantities, the haze precursors form a haze or cloud in the base oil at ambient (or lower) temperatures, particularly if the base oil is allowed to stand at the low temperature for some time (e.g., overnight). The base oil may develop a hazy appearance even after being dewaxed to a low pour point (e.g., less than xe2x88x925xc2x0 C.). The haze will generally be the color of the base oil in which it forms and is usually white when present in otherwise colorless oil. While the haze generally has little or no effect on the performance of the base oil as a lubricating oil base stock, its presence suggests degraded visual quality and possible poor low temperature performance.
Bright Stock feed contains very heavy wax molecules that are difficult to isomerize and that form a haze in the isomerized product. Catalytic dewaxing of waxy Bright Stock (typically 1000xc2x0 F.+) has been found to be very difficult due to the unacceptably high cloud point in the product (where the cloud is attributed to the residual wax). An acceptable cloud point is usually about 0xc2x0 C. or less. In order to reduce the cloud point even near an acceptable level, increased conversion in the dewaxing (e.g., isodewaxing) reactor is required. This increased conversion not only reduces yield of the desired product but also reduces viscosity, thereby lowering the value of the lube.
There is a need in the art for an improved process for producing a low haze heavy base oil.
The present invention relates to processes for producing lubricating base oils with low haze. In one aspect of the present invention, a process for producing a low haze heavy base oil is provided comprising the steps of: (a) providing a heavy waxy feed stream having an initial boiling point greater than 900xc2x0 F. and having a paraffin content of at least 80%; (b) separating the heavy feed stream into a heavy fraction and a light fraction by a deep cut distillation; and (c) hydroisomerizing the light fraction to produce a low haze heavy base oil.
In another aspect of the present invention, a process for producing a low haze heavy base oil is provided that uses a heavy Fischer-Tropsch waxy feed. The process comprises the steps of: (a) providing a heavy Fischer-Tropsch waxy feed; (b) separating the heavy Fischer-Tropsch waxy feed into a first light fraction and a first heavy fraction by atmospheric distillation; (c) separating the first heavy fraction into a second light fraction and a second heavy fraction by vacuum distillation (d) separating the second heavy fraction into a third light fraction and a third heavy fraction by a deep cut distillation; and (e) hydroisomerizing the third light fraction to produce a low haze heavy base oil. The second heavy fraction of step (c) has an initial boiling point greater than 900xc2x0 F. and has a paraffin content of at least 80%.
In yet another aspect of the present invention, a process for producing a low haze heavy base oil is provided that also uses a heavy Fischer-Tropsch waxy feed. The process comprises the steps of: (a) providing a heavy Fischer-Tropsch waxy feed; (b) separating the heavy Fischer-Tropsch waxy feed into a first light fraction and a first heavy fraction by atmospheric distillation at a cut point in the range of 600xc2x0-750xc2x0 F.; (c) separating the first heavy fraction into a second light fraction and a second heavy fraction by vacuum distillation at a cut point in the range of 950xc2x0-1100xc2x0 F.; (d) separating the second heavy fraction into a third light fraction and a third heavy fraction by a deep cut distillation at a cut point in the range of 1200xc2x0-1300xc2x0 F.; and (e) hydroisomerizing the third light fraction to produce a low haze heavy base oil. The second heavy fraction has a paraffin content of at least 80%, and the hydroisomerization of step (e) is carried out at a temperature from 200xc2x0 C. to 475xc2x0 C., at a pressure from 15 psig to 3000 psig, at a liquid hourly space velocity from 0.1 hrxe2x88x921 to 20 hrxe2x88x921, and in the presence of hydrogen at a hydrogen to feed ratio from 500 SCF/bbl to 30,000 SCF/bbl.
In still yet another aspect of the present invention, a process for producing a low haze heavy base oil and a high valued wax is provided comprising the steps of: (a) providing a heavy waxy feed stream having an initial boiling point greater than 900xc2x0 F. and having a paraffin content of at least 80%; (b) separating the heavy feed stream into a heavy fraction and a light fraction by a deep cut distillation; and (c) hydroisomerizing the light fraction to produce a low haze heavy base oil. The heavy fraction separated in step (b) is a high valued wax.
In still yet another aspect of the present invention, a process for producing a low haze heavy base oil and a high valued wax is provided comprising the steps of: (a) providing a heavy waxy feed stream having an initial boiling point greater than 900xc2x0 F. and having a paraffin content of at least 80%; (b) separating the heavy feed stream by a deep cut distillation and recovering a heavy fraction which is less than 30% w/w of the heavy feed stream and a light fraction which is greater than 70% w/w of the heavy feed stream; and (c) hydroisomerizing the light fraction to produce a low haze heavy base oil. The heavy fraction separated in step (b) is a high valued wax.
Definitions
Unless otherwise stated, the following terms used in the specification and claims have the means given below:
xe2x80x9cFischer-Tropsch waxxe2x80x9d means the portion of a Fischer-Tropsch syncrude that contains at least 10% C20 and higher hydrocarbonaceous compounds, preferably at least 40% C20 and higher hydrocarbonaceous compounds and most preferably at least 70% C20 and higher hydrocarbonaceous compounds. Fischer-Tropsch wax is most often a solid at room temperature.
xe2x80x9cDistillate fuelxe2x80x9d means a material containing hydrocarbons with boiling points between approximately 60xc2x0 F. to 1100xc2x0 F. The term xe2x80x9cdistillatexe2x80x9d means that typical fuels of this type can be generated from vapor overhead streams from distilling petroleum crude. In contrast, residual fuels are generally not vaporizable and therefore cannot be generated from vapor overhead streams by distilling petroleum crude. Within the broad category of distillate fuels are specific fuels that include: naphtha, jet fuel, diesel fuel, kerosene, aviation gas, fuel oil, and blends thereof.
The presence of haze in materials of the present process may be determined using a cloud point measurement, such as ASTM-D5773. By xe2x80x9clow hazexe2x80x9d means a cloud point of 10xc2x0 C. or less. Preferably, the cloud point of the low haze heavy base oil is 5xc2x0 C. or less, more preferably 0xc2x0 C. or less.